The invention relates to a vibration damper for vehicles of the type which has a piston and cylinder with fluid medium therein and having valve controls to control the medium flow between two cylinder spaces during relative movements of the piston and cylinder.
A vibration damper of this type is disclosed in German Published Unexamined Application No. (DE-OS) 34 21 601. In the case of this construction, the connecting duct that extends through the working piston has the purpose of admitting damping fluid to spring disks that cover valve bores of damping valves of the working piston, for the reduction of damping forces or for the softening of the damping against its closing force. This can be controlled arbitrarily from the driver's seat by means of the valve element that is adjustably arranged in the piston rod, for the opening and closing of the connecting duct.
In the case of this vibration damper, an adjustment of the damping forces is provided only for the tension stage. In addition, the construction is operable only in connection with the spring disks of the piston damping valves.
In addition, it requires a special equipping of the working piston with front-side recesses that are to be assigned to valve bores for the tension phase and that are to be connected with the connecting duct.
Other prior vibration dampers are disclosed in German Utility Model No. (DE-GM) 1858 547; German Published Examined Application No. (DE-AS) 1181 074; and German Patent No. (DE-PS) 869,717.
The invention is based on the objective of improving a vibration damper of the above-noted type in such a way that for the tensile stage as well as for the compression stage, a defined damping force reduction of varying intensity can be selected. In this case, the changing of the damping force should be possible independently of the development of the working piston.
This objective is achieved in a special control piston construction for controlling the communication between the cylinder spaces of the camper. In the case of the construction according to preferred embodiments of the invention, the change of damping force takes place exclusively by means of two throttles that are arranged in the connecting duct of the piston rod forming a bypass that is independent of the working piston. The special development of the damping valves of the working piston may therefore be arbitrary. Since in this case, the throttle that has the larger throttling resistance in the connecting duct pressure-dependently is arranged so that it can be moved back and forth between a passage position and a throttling position, the throttle having the lower throttling resistance becomes effective as soon as, during one of the two movements of the working piston, the movable throttle is steered from its throttling position in the direction of the passage position. By means of the corresponding dimensioning of the throttle cross-sections, a desired damping force reduction can be preselected for each operating stage.
Preferably, the movable throttle in this case determines the throttling resistance for the tensile stage.
The invention is equally advantageously suitable for single-tube and double-tube dampers as well as for the shock absorber of a hydropneumatic wheel suspension.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.